Anesthesiologists use alpha2 adrenergic agonists to facilitate the anesthetic management of the surgical patient since drugs of this class (e.g. clonidine and dexmedetomidine) exhibit sedative, anxiolytic, analgesic, and hemodynamic-stabilizing properties. The alpha2 adrenergic agonists also reduce the need for, and the complications associated with, other anesthetic agents. Work described in this application will determine whether alpha2 adrenergic agonists (i) protect against the effects of cerebral ischemia in animals and cell culture. The more prolonged administration of alpha 2 agonists in the perioperative period raises the question whether (ii) tolerance develops to the anesthetic properties of alpha2 agonists. Lastly, work in this application will address the (iii) mechanism for the synergistic interaction between alpha2 adrenergic agonists and benzodiazepines. The neuroprotective effects of alpha2 agonists alone and in combination with other neuroprotective agents will be assessed by following the development of ischemic neuronal damage in both a cell culture system and in an animal model of focal ischemia. The time course from the development of tolerance to the anesthetic effects of alpha2 agonists will be examined in behavior paradigms. Subsequently, the characteristics of tolerance-producing alpha2 agonists, and whether cross- tolerance develops to other inhibitory neurotransmitter receptor agonists, will be tested in behavior models. The expression and function of key molecular components in the alpha2 adrenergic receptor-effector pathway will be analyzed biochemically in the alpha2 tolerant state. To uncover the mechanism for the synergistic interaction alpha2 adrenergic agonists and benzodiazepines, the in vivo hypnotic effects of a combination of alpha2 agonists and benzodiazepine type I receptor agonists will be determined. The binding kinetics of GABA and alpha2 agonists will be examined in the presence of the other receptor ligand using radiolabeled binding techniques. Finally, the effect of alpha2 agonists on enhancers (benzodiazepines) and attenuators (desensitizing agents) of GABA-mediated chloride flux will be examined in a synaptosomal preparation. These studies will define the actions, drug interactions, and clinical profile for the anesthetic use of alpha2 agonists.